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  <h1>Overview</h1>

  <p>Smack is a library for client-to-server XMPP connections to perform real-time communications and data exchange. This includes, but is not limited to, instant messaging and group chat. More generically speaking, it allows you to easily exchange data in various ways: For example fire-and-forget, publish-subscribe, between human and non-human endpoints. The use cases include M2M, IoT, and many more.</p>

  <p>Smack is a pure Java library, open-source and highly modular. It runs on Android and Java SE. The API strives to be easy to use but yet powerful.</p>

  <h2>Key Advantages</h2>

  Smack is extremely simple to use, yet provides a powerful API. Sending a text message to a user can be accomplished in only a few lines of code.

  <pre>{@code
AbstractXMPPConnection connection = new XMPPTCPConnection("mtucker", "password", "jabber.org");
connection.connect().login();

Message message = connection.getStanzaFactory()
   .buildMessageStanza()
   .to("jsmith@igniterealtime.org")
   .setBody("Howdy! How are you?")
   .build();

connection.sendStanza(message);

connection.disconnect();
}</pre>

  <p>Smack doesn't force you to code at the protcol level of XMPP. The library provides intelligent higher level constructs, often called {@link org.jivesoftware.smack.Manager}, which let you program more efficiently. Other examples of those constructs are the Chat and Roster classes.</p>

  <p>Smack comes with APIs for easy machine-to-machine communication. You can set any number of properties on each message, including properties that are Java objects.</p>

  <h2>License</h2>

  <p>Smack is open-source and most parts are under the Apache License
  2.0, which means you can incorporate Smack into your commercial or
  non-commercial applications. Some parts of Smack may be under a
  different open-source license. Please refer to the individual
  subprojects for their license statement.</p>

  <p>Note that the Apache License 2.0 requires that the contents of a
  NOICE text file are shown "…within a display generated by the
  Derivative Works, if and wherever such third-party notices normally
  appear.". Smack comes with such a NOTICE file. The content of
  Smack's NOTICE file can conveniently be retrieved using
  {@link org.jivesoftware.smack.Smack#getNoticeStream}.</p>

  <h2>About XMPP</h2>

  <p>XMPP (eXtensible Messaging and Presence Protocol) is an open protocol standardized by the <a href="https://ietf.org/">Internet Engineering Task Force (IETF)</a> and supported and extended by the <a href="https://www.xmpp.org/">XMPP Standards Foundation (XSF)</a>.</p>

  <h2>Smack Modules</h2>

  <p>Smack is meant to be easily embedded into any existing Java
	application. The library ships as several modules to provide more
	flexibility over which features applications require.</p>

  <ul>
  <li>smack-core -- provides core XMPP functionality. All XMPP features that are part of the XMPP RFCs are included.</li>
  <li>smack-im -- provides functionality defined in RFC 6121 (XMPP-IM), like the Roster.</li>
  <li>{@link org.jivesoftware.smack.tcp smack-tcp} -- support for XMPP over TCP. Includes XMPPTCPConnection class, which you usually want to use</li>
  <li>smack-extensions -- support for many of the extensions (XEPs) defined by the XMPP Standards Foundation, including multi-user chat, file transfer, user search, etc. The extensions are documented in the [extensions manual](extensions/index.md).</li>
  <li>smack-experimental -- support for experimental extensions (XEPs) defined by the XMPP Standards Foundation. The API and functionality of those extensions should be considered as unstable.</li>
  <li>smack-legacy -- support for legacy extensions (XEPs) defined by the XMPP Standards Foundation.
  <li>smack-bosh -- support for BOSH (XEP-0124). This code should be considered as beta.</li>
  <li>smack-resolver-minidns -- support for resolving DNS SRV records with the help of <a href="https://minidns.org">MiniDNS</a>. Ideal for platforms that do not support the javax.naming API. Also supports [DNSSEC](dnssec.md) TODO: Fix link.</li>
  <li>smack-resolver-dnsjava -- support for resolving DNS SRV records with the help of dnsjava.</li>
  <li>smack-resolver-javax -- support for resolving DNS SRV records with the javax namespace API.</li>
  <li>smack-debug -- an enhanced GUI debugger for protocol traffic. It will automatically be used when found in the classpath and when [debugging](debugging.md) is enabled.</li>
  </ul>

  <h2>Main API Entry Points</h2>

  <ul>
    <li>{@link org.jivesoftware.smack.XMPPConnection}</li>
    <li>{@link org.jivesoftware.smack.tcp.XMPPTCPConnection}</li>
    <li>{@link org.jivesoftware.smack.roster.Roster}</li>
    <!-- <li>{@link org.jivesoftware.smack.chat2.Chat}</li> -->
    <!-- More form index.md -->
  </ul>

  <h2>Smack Extensions</h2>

  <p>
	Since the X in XMPP stands for eXstensible, Smack comes with many
	built-in extensions for XMPP. Click
  </p>
  <blockquote><b>{@link org.jivesoftware.smackx}</b></blockquote>
  <p>
	for an overview of all supporteted XMPP extensions of Smack.
  </p>

  Some selected extensions are
  <ul>
    <li>{@link org.jivesoftware.smackx.muc.MultiUserChat Multi-User Chat (XEP-0045)}</li>
    <li>{@link org.jivesoftware.smackx.carbons.CarbonManager Message Carbons (XEP-0289)}</li>
    <li>{@link org.jivesoftware.smackx.omemo OMEMO (XEP-0384)}</li>
    <!-- <li>{@link org.jivesoftware.smack.chat2.Chat}</li> -->
    <!-- More form index.md -->
  </ul>

  <h2>Configuration</h2>

  <p>Smack has an initialization process that involves 2 phases.</p>

  <ul>
	<li>Initializing system properties - Initializing all the system properties accessible through the class **SmackConfiguration**. These properties are retrieved by the _getXXX_ methods on that class.</li>
	<li>Initializing startup classes - Initializing any classes meant to be active at startup by instantiating the class, and then calling the _initialize_ method on that class if it extends **SmackInitializer**. If it does not extend this interface, then initialization will have to take place in a static block of code which is automatically executed when the class is loaded.</li>
  </ul>

  <p>
	Initialization is accomplished via a configuration file.
	By default, Smack
will load the one embedded in the Smack jar at _org.jivesoftware.smack/smack-
	config.xml_.
	This particular configuration contains a list of initializer
	classes to load.
	All manager type classes that need to be initialized are
	contained in this list of initializers.
  </p>

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